Recognition of normal components in the body by the immune system leads to autoimmunity. Autoimmune aggression results in severe diseases, such as multiple sclerosis, Lupus, diabetes, and many others. In a healthy individual, cells of the immune system are educated to ignore or tolerate its own host (referred to as self) and to recognize and react to foreign proteins (antigens). Central to this self/nonself discrimination are the T cells, a group of white blood cells that circulate throughout the body. Recognition of foreign antigens by T cells occurs only if the antigen is presented to the T cell by an antigen-presenting cell (APC). The first step in most immune responses is the presentation of antigen by an APC to a CD4 T cell. Such T cells recognize a cell surface complex composed of a fragment from the foreign protein that is bound to a class II histocompatibility molecule (MHC class II) on the APC. The purpose of this work is to determine what leads to the recognition of a self protein by CD4 T cells, and what types of self proteins may trigger autoimmune attack. A better understanding of these processes and of the proteins involved would facilitate the development of treatments to avoid or counteract autoimmune reactions. This work studied presentation to CD4 T cells of myelin basic protein, a suspected self protein involved in multiple sclerosis. An unusual mode of presentation was described for this autoantigen. Furthermore, a new and unsuspected source of potential autoantigens has been described.